The present invention is directed to a method for manufacturing a trench capacitor of a one-transistor memory cell in a semiconductor substrate that is arranged overlapping relative to an insulating field oxide.
One-transistor memory cells utilized for VLSI semiconductor circuits have capacitors for storing information, these capacitors being fashioned as trench capacitors in a semiconductor substrate of, for example, silicon for minimizing the space requirement. A conventional embodiment of such trench capacitors is known from the book by Widmann, Mader and Friedrich, "Technologie hochintegrierter Schaltungen", Springer-Verlag 88, page 270 and is also disclosed by European reference EPA 0 187 596 in the embodiment referred to as "stacked trench capacitor (STT)". A first electrode of the trench capacitor is formed either by the substrate that is locally re-doped for this purpose (conventional trench capacitor) or is formed by a conductive layer located on the inside trench wall (STT). The second or capacitor plate electrode is formed by a conductive layer with which the trench is filled after the first electrode has been clad with a dielectric layer. For further reducing the space requirement, it is also proposed in European reference EPA 0 187 596 to arrange the trench overlapping with respect to an insulating field oxide that insulates the individual cells of a semiconductor memory arrangement and partially covers the semiconductor surface and, in particular, to etch the trench into the substrate through the edge region of the field oxide.
Given such trench capacitors, the conductive layer that is usually composed of polycrystalline silicon and from which the capacitor plate electrode is formed must be structured using a phototechnique, i.e. must be in turn locally removed with, for instance, a dry etching process. The adjustment precision connected with the phototechnique impedes an arbitrary reduction in the space occupied by the capacitor, so that the integration density of such memory cells cannot be further increased.